Retrospective analysis algorithm for identifying and localizing residual reserves of the developed multilayer oil field

Long-term phased development of a multi-layer field, including tens and hundreds of oil-bearing horizons and local deposits, combined with their vertical and horizontal separation, creates conditions for the formation of residual oil reserves. For the purpose of identifying and spatial localization of residual reserves, an algorithm for retrospective analysis was developed and applied on the example of the Upper and Lower Devonian terrigenous deposits of the Romashkinskoe oil field, which have been developed since 1952. The long history of geological study and development of oil-bearing formations of the Pashiysky D1 (layers g and e), Mullinsky D2, Ardatovsky D3, Vorobyevsky D4 and Biysky D5 horizons is analyzed according to the data of 2605 wells. It is proposed to single out 6 categories of formations and the reserves contained in them. Previously undeveloped formations composed of conditioned reservoirs are classified as category 1. Formations composed of more clayey and less permeable reservoirs are awarded with category 2. Category 3 includes previously developed formations, but left before reaching the limit of water cut, and category 4 – currently being developed intervals. The least promising are those that are stopped after reaching the maximum water cut (category 5), as well as wedged out, replaced by non-reservoirs or considered water-bearing (category 6) formations. Categories were mapped to identify, visualize and describe the main patterns in the distribution of residual reserves, which are established both in single wells and in bypassed oil that include a group of wells. The algorithm was tested on the corporate information base of historical data on geological exploration, research and development of the Abdrakhmanovskaya area of ​​the Romashkinskoe oil field. Examples of experimental workover operations to include the identified residual reserves in the development are given.